Autonomous driving of a motor vehicle means driving of the motor vehicle independently of a driver to different extents. A distinction is drawn between up to six stages, rising in level of autonomy of the motor vehicle, wherein the lowermost stage still comprises pure operator control by the driver and the topmost stage no longer requires any intervention by a driver at all. Starting from a stage which is identified as high-level automation, driving which is executed largely autonomously by the motor vehicle is assumed. Important functions, such as, for example, a traction system which, in the case of an electric vehicle, comprises, for example, an electric motor, a line system which carries power to said electric motor, and a drive battery, are autonomously monitored for the purpose of operating the motor vehicle.
Electric vehicles which are customary at present, including electric hybrid vehicles and battery-electric vehicles, have a drive voltage of up to 400 V. Accordingly, without limiting the generality, a high-voltage battery which is carried in the vehicle as an energy supply, generally a battery in the form of a certain number of secondary cells which are connected in series, is designed for this voltage level. Charging stations which are accessible in public areas also provide a charging voltage of 400 V as standard. In contrast, it is generally advantageous to work with voltages of, for example, 800 V or even 1200 V in electric utility vehicles, sports cars and racing vehicles in order to provide a required drive power of more than 250 kW. In order to save on weight due to switching systems which would first have to raise an on-board voltage to a level of this kind, it is advantageous to likewise operate a high-voltage battery in this voltage range. However, this in turn requires switching systems which step up the voltage of 400 V provided by the charging stations to the voltage of the high-voltage battery. In the prior art, this is achieved by voltage converters and, in particular, DC/DC converters, so-called DC/DC boosters, which establish a desired voltage level, for example of the high-voltage battery at 800 V, from a prespecified voltage level, for example of the charging station at 400 V.
Furthermore, it is possible in the prior art to connect the secondary cells of a battery in parallel in a plurality of groups, down to an actuation of an individual cell. The voltage level is therefore lower than would result from a total voltage of all of the secondary cells being connected in series. A method of this kind is disclosed in document US 2013 0106 357 A1, which is incorporated by reference herein, in which series or parallel interconnection is controlled by means of use of one switching contactor for each respective group in accordance with a state of discharge of a respective group of secondary cells.
Dividing a battery into suitable groups of secondary elements on the basis of an available charge current is carried out in document US 2012 0013 303 A1, which is incorporated by reference herein, by a charging control unit, this in turn resulting in parallel connection of the groups and the use of electronic components with the abovementioned disadvantages.
The applicant themselves cite DE 10 2013 102 576 A1, which is, incorporated by reference herein, which brings into play the advantages of a multiple charge connection. Therefore, explicitly in the case of a high-voltage battery of 800 V, a charging process can be carried out more rapidly with two charge connections of 400 V, however two charging stations also have to be available for this purpose.